The present invention relates to microfluidic devices and, more particularly, to a micropump that is electrically driven by a change of surface tension at an electrical double layer interface between two immiscible electrolyte fluids configured within a capillary.
The present invention is constructed in a similar manner to the mercury/electrolyte-based electrochemical micropump illustrated in U.S. Pat. No. 5,472,577, issued to Porter et al, on Dec. 5, 1995 for FLUID PUMPING SYSTEM BASED ON ELECTROCHEMICALLY-INDUCED SURFACE TENSION CHANGES. In the prior invention, the well-known surface tension change at the liquid metal (mercury) and the electrolyte interface was utilized as an actuation force for micropumping. Similar types of micropumping have received enormous interest, as described in xe2x80x9cMicrofluidicsxe2x80x94A Reviewxe2x80x9d, by Gravesen, P., Branebjerg, J., and Jensen, O. S., Journal of Micromechanical and Microengineering 3, 168 (1993).
The micropump of the prior invention, while well constructed, leaves room for improvement because it uses mercury which is potentially hazardous.
The search for a more practical microfluidic system has spawned the current micropump. The present invention utilizes two immiscible electrolyte liquids, disposed within a capillary tube. The two immiscible liquid phases of the micropump can comprise a salt in an aqueous solution and an organic liquid, for example. The variation of electrical potentials at the interface is determined by the distribution of ionic/dipolar components in the liquids. Across the interface, there is an excess electrical charge on one side, and an excess opposite charge on the other side. The excess charge occurs by reason of electroneutrality, resulting in an electrical double layer with electrochemically controllable interfacial tension. The invention uses a change in surface tension across the interface as the driving force for operating the pump.
The organic liquid phase of the micropump can comprise, for example, 1, 2-dichloroethane with tetraphenylammonium tetra-phenylborate as an electrolyte (phase-1), which is in contact with an aqueous solution of sodium chloride (phase-2). Each of the liquids is disposed in a glass capillary. The liquids form a clear immiscible boundary.
Two platinum wires are inserted into the liquids from each side of the boundary, respectively, and serve as two electrodes. The interfacial tension changes when an alternating voltage (e.g., a square waveform with 1xcx9c3 volts amplitude) is applied to the two electrodes. The voltage alternation causes the boundary line to move back and forth, creating a piston-type action. The magnitude of the piston displacement depends on the magnitude and the frequency of the alternating voltage. For example, a displacement up to 4 mm was demonstrated in a capillary having a 1 mm diameter, powered by a square-wave voltage of 2 volts having a 1 Hz frequency.
In comparison with many current micropump devices utilizing thermoneumatic, piezoelectric, and electroosmotic actuation, the present invention has lower power requirements. In addition, it is relatively easy to construct and integrate into small devices. In addition, the fluid components in the device can be provided by a relatively large selection of environmentally-friendly materials, an advantage desirable in terms of micro-fabrication, integration and biocompatibility.
In accordance with the present invention, there is provided a micropump for microfluidic applications. The micropump is configured as a glass capillary containing a pair of immiscible electrolyte liquids. The micropump operates on a principle of surface tension change at the electrical double layer interface between the two immiscible electrolyte liquids. The device generates fluid displacements when subjected to a small, alternating voltage. One of the immiscible liquids (phase-1) comprises an organic electrolyte (e.g., dichloroethane with tetraphenylammonium tetraphenylborate). The other immiscible liquid (phase-2) comprises an aqueous solution of sodium chloride. The liquids form a clear immiscible boundary.
Two platinum wires are inserted into the liquids from each side of the boundary, respectively, serving as two electrodes. The interfacial tension changes when an alternating voltage (e.g., a square waveform with 1xcx9c3 volts amplitude) is applied to the two electrodes. The voltage alternation causes the boundary line to move back and forth, creating a piston-type action. The magnitude of the piston displacement depends on the magnitude and the frequency of the alternating voltage.
It is an object of this invention to provide an improved microfluidic device.
It is another object of the invention to provide a micropump that uses interfacial surface tension between two immiscible electrolyte liquids to provide a pumping force generated by an applied alternating voltage.